The invention is directed to a method and apparatus for forming a carbonaceous hard film and a device therefor. In particular, the invention is directed to a method and apparatus for forming a novel carbonaceous hard film having a dramatic surface-improving effect, which is useful in tools and moving parts where a high hardness, wear resistance, and reduced friction are required, and in precision electronic instrument parts and the like.
In recent years, higher hardness and higher functionality are being required more and more from hard coatings for industrial use. In these circumstances, hard carbonaceous coatings, represented by diamond-like carbon films, have drawn attention as a material satisfying the more rigorous demands of a new era. Such hard carbonaceous coatings have been subject to attempts at vapor phase film deposition by various methods, foremost among them chemical vapor deposition (CVD), but there are various problems in the path to practical use, and the range of application has been limited so far.
For example, in the most successful instances, a maximum level of 3,000 kg/mm2 Vickers hardness has been attained in a hard carbonaceous film through plasma assisted CVD methods, but a problem exists in that 3,000 kg/mm2 has been an actual limit. Adhesion characteristics and the substrate temperature during film formation also present problems to be solved with regard to conventional hard carbonaceous films resulting from vapor phase film deposition.
In hard carbonaceous films formed using plasma enhanced CVD processes, adhesion characteristics to various steel and other metallic substrate materials, primarily tools, are in reality poor, and implementation into practical applications has been problematic. The reason is that the coefficient of thermal expansion of a hard carbonaceous film is extremely low (0.80xc3x9710xe2x88x926/K). Thus, when a film is formed on a substrate material with a large coefficient, such as stainless steel (13.8xc3x9710xe2x88x926/K in primary material, iron), it has not been possible to avoid reaching relatively high temperatures in the substrate material during formation of the hard carbonaceous film. When the substrate material temperature cools down from the high temperature reached during film-formation to ambient temperature after film-formation, stress develops between the film and the substrate material, and consequently the film peels off.
Conventional methods investigated for improving the poor adhesion of a film include forming an intermediate layer between the substrate material and the film (a silicon compound or the like), and roughening of the substrate material surface. However, while the first method initially appears to improve adhesion between the hard carbonaceous film and the intermediate layer, in actual application in tools and the like, adhesion has still been insufficient, and the film peels off. It has also not been possible to obtain an intermediate layer having a sufficient hardness to allow placement under a high-hardness carbonaceous film. The second method, like the first method, does not obtain adequate adhesion strength in actual use.
During film-formation, a substrate heating temperature of at least 200xc2x0 C. or more has been required to obtain a high-hardness carbonaceous film. Thus, it has not been practical to apply hard carbonaceous films to substrate materials that experience deformation or deterioration at high temperatures, e.g., substrate materials having a low melting point or that become annealed and lose their hardness within this range of temperatures.
In various conventional CVD processes, gas mixtures of hydrogen and methane, or other hydrocarbon gases, have been used as the source for film formation material and the incorporation of hydrogen into the carbonaceous film was deliberate. However, as noted above, the hardness thus obtained has been merely 3,000 kg/mm2 Vickers hardness at maximum. In terms of heat-resistance, in hard carbonaceous films containing hydrogen, graphitization begins at 350xc2x0 C., whereas in a film not containing hydrogen, graphitization does not begin unless the temperature is 500xc2x0 C. or higher. The onset of graphitization causes a decline in hardness and a degradation of characteristics.
With hydrogen, the danger of ignition is also extremely high, and use of methane gas or other such hydrocarbon gas at the same time presents a flammability hazard.
Methods for forming a hard carbonaceous film not containing hydrogen include sputtering methods, electron beam deposition methods, and direct ion beam methods, but in these methods, hardness, wear resistance, and other such characteristics have been found to be inadequate, and for reasons including the narrow range of parameters in which the film-forming process operates an article adequate for practical use cannot presently be obtained.
CVD methods and other such plasma processes also entail problems in that generation of films having a uniform, large surface area has been difficult. When plasma is generated adjacent to an insulating hard carbonaceous film, once the plasma has been extinguished, growth does not again appear in the same location even if the plasma is regenerated, thus posing a major problem to the creation of a large, uniform surface area film.
Accordingly, the invention provides a method and apparatus for forming a novel carbonaceous hard film, which has a high hardness surpassing the hardness level previously deemed a conventional limit, is superior in adherence to a substrate material, obviates effects resulting from substrate temperature, and is also superior in potential for creation of a large surface area.
The invention provides a method and apparatus for forming a carbonaceous hard film by irradiation with gas cluster ions during or following the deposition of a layer of carbonaceous material from vapor which may, or not, be partially ionized, wherein said method is a method for vapor phase film deposition of a carbonaceous hard film on a substrate material under a vacuum-reduced pressure. The vaporized carbonaceous material, which may be ionized or non-ionized, is deposited onto a substrate surface. Gas clusters made up of atomic or molecular aggregate of a material, which is gaseous at ambient temperature and pressure, are ionized, accelerated and irradiated onto the surface containing the layer of carbonaceous material.
The invention also provides a formation method, wherein the carbonaceous material is one or more of a fullerene, a carbon nanotube, graphite, amorphous carbon, or a carbene not containing hydrogen. The formation method is such that the atoms or molecules comprising the gas clusters are comprised of one or more of a rare gas, oxygen, a carbon oxide, nitrogen, a nitride, a halogen, or a halide. The Vickers hardness of the carbonaceous hard film is more than 4,000 kg/mm2 and the coefficient of friction is 0.15 or less. In addition, the carbonaceous hard film does not contain hydrogen.
The invention provides an apparatus for forming a carbonaceous hard film on a substrate through irradiation with gas cluster ions, wherein the apparatus is equipped with a gas cluster beam generation means, a gas cluster ionization means, ionized gas cluster acceleration means, means for generating vaporized particles of carbonaceous material, vaporized particles ionization means, means for acceleration of the vaporized and ionized particles of carbonaceous materials, and a film formation unit therefore, which are disposed as necessary, and vacuum exhaust means. The gas cluster ionization and acceleration units and the carbonaceous material vaporized particle product, or the product of ionization and acceleration units added thereto, are directed towards a substrate surface disposed in the film formation unit such that individual gas cluster ions and ionized or non-ionized carbonaceous material vaporized particles are irradiated onto the substrate.
The invention also provides a carbonaceous hard film deposited on a substrate material from vapor phase, wherein the Vickers harness is more than 4,000 kg/mm2 and the coefficient of friction is 0.15 or less, and the invention offers a carbonaceous hard film not containing hydrogen.